Delete a node in a Doubly Linked List

Doubly Link List Set 1| Introduction and Insertion

Write a function to delete a given node in a doubly linked list.

     (a) Original Doubly Linked List

 

     (a) After deletion of head node

 

     (a) After deletion of middle node

 

     (a) After deletion of last node

 



Algorithm
Let the node to be deleted is del.
1) If node to be deleted is head node, then change the head pointer to next current head.
2) Set next of previous to del, if previous to del exists.
3) Set prev of next to del, if next to del exists.

C

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#include <stdio.h>
#include <stdlib.h>
  
/* a node of the doubly linked list */
struct Node {
    int data;
    struct Node* next;
    struct Node* prev;
};
  
/* Function to delete a node in a Doubly Linked List.
   head_ref --> pointer to head node pointer.
   del  -->  pointer to node to be deleted. */
void deleteNode(struct Node** head_ref, struct Node* del)
{
    /* base case */
    if (*head_ref == NULL || del == NULL)
        return;
  
    /* If node to be deleted is head node */
    if (*head_ref == del)
        *head_ref = del->next;
  
    /* Change next only if node to be deleted is NOT the last node */
    if (del->next != NULL)
        del->next->prev = del->prev;
  
    /* Change prev only if node to be deleted is NOT the first node */
    if (del->prev != NULL)
        del->prev->next = del->next;
  
    /* Finally, free the memory occupied by del*/
    free(del);
    return;
}
  
/* UTILITY FUNCTIONS */
/* Function to insert a node at the beginning of the Doubly Linked List */
void push(struct Node** head_ref, int new_data)
{
    /* allocate node */
    struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
  
    /* put in the data  */
    new_node->data = new_data;
  
    /* since we are adding at the begining,
    prev is always NULL */
    new_node->prev = NULL;
  
    /* link the old list off the new node */
    new_node->next = (*head_ref);
  
    /* change prev of head node to new node */
    if ((*head_ref) != NULL)
        (*head_ref)->prev = new_node;
  
    /* move the head to point to the new node */
    (*head_ref) = new_node;
}
  
/* Function to print nodes in a given doubly linked list
   This function is same as printList() of singly linked lsit */
void printList(struct Node* node)
{
    while (node != NULL) {
        printf("%d ", node->data);
        node = node->next;
    }
}
  
/* Drier program to test above functions*/
int main()
{
    /* Start with the empty list */
    struct Node* head = NULL;
  
    /* Let us create the doubly linked list 10<->8<->4<->2 */
    push(&head, 2);
    push(&head, 4);
    push(&head, 8);
    push(&head, 10);
  
    printf("\n Original Linked list ");
    printList(head);
  
    /* delete nodes from the doubly linked list */
    deleteNode(&head, head); /*delete first node*/
    deleteNode(&head, head->next); /*delete middle node*/
    deleteNode(&head, head->next); /*delete last node*/
  
    /* Modified linked list will be NULL<-8->NULL */
    printf("\n Modified Linked list ");
    printList(head);
  
    getchar();
}

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Java

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// Java program to delete a node from
// Doubly Linked List
  
// Class for Doubly Linked List
public class DLL {
    Node head; // head of list
  
    /* Doubly Linked list Node*/
    class Node {
        int data;
        Node prev;
        Node next;
  
        // Constructor to create a new node
        // next and prev is by default initialized
        // as null
        Node(int d) { data = d; }
    }
  
    // Adding a node at the front of the list
    public void push(int new_data)
    {
        // 1. allocate node
        // 2. put in the data
        Node new_Node = new Node(new_data);
  
        // 3. Make next of new node as head
        // and previous as NULL
        new_Node.next = head;
        new_Node.prev = null;
  
        // 4. change prev of head node to new node
        if (head != null)
            head.prev = new_Node;
  
        // 5. move the head to point to the new node
        head = new_Node;
    }
  
    // This function prints contents of linked list
    // starting from the given node
    public void printlist(Node node)
    {
        Node last = null;
  
        while (node != null) {
            System.out.print(node.data + " ");
            last = node;
            node = node.next;
        }
  
        System.out.println();
    }
  
    // Function to delete a node in a Doubly Linked List.
    // head_ref --> pointer to head node pointer.
    // del --> data of node to be deleted.
    void deleteNode(Node head_ref, Node del)
    {
  
        // Base case
        if (head == null || del == null) {
            return;
        }
  
        // If node to be deleted is head node
        if (head == del) {
            head = del.next;
        }
  
        // Change next only if node to be deleted
        // is NOT the last node
        if (del.next != null) {
            del.next.prev = del.prev;
        }
  
        // Change prev only if node to be deleted
        // is NOT the first node
        if (del.prev != null) {
            del.prev.next = del.next;
        }
  
        // Finally, free the memory occupied by del
        return;
    }
  
    // Driver Code
    public static void main(String[] args)
    {
        // Start with the empty list
        DLL dll = new DLL();
  
        // Insert 2. So linked list becomes 2->NULL
        dll.push(2);
  
        // Insert 4. So linked list becomes 4->2->NULL
        dll.push(4);
  
        // Insert 8. So linked list becomes 8->4->2->NULL
        dll.push(8);
  
        // Insert 10. So linked list becomes 10->8->4->2->NULL
        dll.push(10);
  
        System.out.print("Created DLL is: ");
        dll.printlist(dll.head);
  
        // Deleting first node
        dll.deleteNode(dll.head, dll.head);
  
        // List after deleting first node
        // 8->4->2
        System.out.print("\nList after deleting first node: ");
        dll.printlist(dll.head);
  
        // Deleting middle node from 8->4->2
        dll.deleteNode(dll.head, dll.head.next);
  
        System.out.print("\nList after Deleting middle node: ");
        dll.printlist(dll.head);
    }
}

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Python

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# Program to delete a node in doubly linked list
  
# for Garbage collection
import gc
  
# A node of the doublly linked list
class Node:
      
    # Constructor to create a new node
    def __init__(self, data):
        self.data = data 
        self.next = None
        self.prev = None
  
class DoublyLinkedList:
     # Constructor for empty Doubly Linked List
    def __init__(self):
        self.head = None
   
   # Function to delete a node in a Doubly Linked List.
   # head_ref --> pointer to head node pointer.
   # dele --> pointer to node to be deleted
  
    def deleteNode(self, dele):
          
        # Base Case
        if self.head is None or dele is None:
            return 
          
        # If node to be deleted is head node
        if self.head == dele:
            self.head = dele.next
  
        # Change next only if node to be deleted is NOT
        # the last node
        if dele.next is not None:
            dele.next.prev = dele.prev
      
        # Change prev only if node to be deleted is NOT 
        # the first node
        if dele.prev is not None:
            dele.prev.next = dele.next
        # Finally, free the memory occupied by dele
        # Call python garbage collector
        gc.collect()
  
  
    # Given a reference to the head of a list and an
    # integer, inserts a new node on the front of list
    def push(self, new_data):
   
        # 1. Allocates node
        # 2. Put the data in it
        new_node = Node(new_data)
   
        # 3. Make next of new node as head and
        # previous as None (already None)
        new_node.next = self.head
   
        # 4. change prev of head node to new_node
        if self.head is not None:
            self.head.prev = new_node
   
        # 5. move the head to point to the new node
        self.head = new_node
  
  
    def printList(self, node):
        while(node is not None):
            print node.data,
            node = node.next
  
  
# Driver program to test the above functions
  
# Start with empty list
dll = DoublyLinkedList()
  
# Let us create the doubly linked list 10<->8<->4<->2
dll.push(2);
dll.push(4);
dll.push(8);
dll.push(10);
  
print "\n Original Linked List",
dll.printList(dll.head)
  
# delete nodes from doubly linked list
dll.deleteNode(dll.head)
dll.deleteNode(dll.head.next)
dll.deleteNode(dll.head.next)
# Modified linked list will be NULL<-8->NULL
print "\n Modified Linked List",
dll.printList(dll.head)
  
# This code is contributed by Nikhil Kumar Singh(nickzuck_007)

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Output:

Original Linked list 10 8 4 2 
 Modified Linked list 8

Time Complexity: O(1)
Time Complexity: O(1)

Please write comments if you find any of the above codes/algorithms incorrect, or find better ways to solve the same problem.



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